HISTORY OF GEODETIC OPERATIONS IN RUSSIA. 313 



this purpose iu 1874, came to the conclusion that the Aral Sea is liij^lior 

 than the Caspian by 243 feet. 



In 1871, systematic spirit leveling was begun, and in its prosecution 

 many interesting facts have been brought to light. One of these is the 

 diflerent levels of the water in the Baltic Sea. Taking for the level 

 of water at Cronstadt, the height of the sea level proves to be : 



Metres. 



At Revol - 0.57 



At Dinaniiude — 0,88 



At Libau — 1.24 



Another is the discrepancy between spirit levelling and geodetic level- 

 ling in obtaining the elevation of the threshold of the Dorpat Observa- 

 tory. This amounts to nearly 4 metres, and is suggestive of a consid- 

 erable local disturbance. 



The first local attraction observed in Russia was iu the neighborhood 

 of Moscow, where, owing to the absence of hills, one might least ex- 

 pect a discrepancy between geodetic and astronomic results. Soon 

 after the completion of the triaugulation in the province of Moscow 

 this deflection attracted public attention, and the astronomer Schweizer 

 undertook a special investigation. The result showed that in this 

 province, almost in the direction from east to west, there is a strip along 

 whose northern boundary there is a considerable (/') northern deflec- 

 tion, and on the southern border a southerly deflection of 10". It is 

 supposed that alo ng this belt there must be a vast extent of matter of 

 comparatively small density, or underlying it great cavities. 



The most elaborate investigation of local deflection of the plumb line 

 was made in the Caucasus by General Stebnizki and published in the 

 Memoirs of the St. Petersburg Academy of Sciences for 1870. From 

 the analysis of the astronomic and trigonometric operations executed 

 on both sides of the principal Caucasian ridge it became evident that, 

 iu general, to the north of the mountains there exists a deflection to 

 the south and on the south an opposite deflection. The greatest dis- 

 crepancies in the astronomic and geodetic latitudes i)roved to be in 

 Vladikaukasus, — .3.5".76; in Alexandrovsknja, — 18".14 ; in Petrovk, 

 — 18"..j6; and in Dushet, +18". 29. Availing himself of the surveys 

 already executed furnishing a great number of very actmrately deter- 

 mined points. General Stebnizki computed the eflect which the attrac- 

 tion of the exterior mountainous mass would have upon the astronomic 

 latitude of the different stations. In these computations no attracting 

 mass was considered which was distant more than 240 versts, while the 

 chief disturbing causes were frequently found to lie within a circle with 

 a radius of 80 versts, the station occupying the central point. It was 

 found that the greater part of tiie noted discrepancies were sufficiently 

 accounted for by the law of attraction having regard to the exterior 

 mass alone. In the cases just cited tlie computed differences reduced 

 the station errors to 3", -1' .31, -f 2". 15 and — U".80. iiut there are other 



